Separating of optical integrated modules and structures formed thereby

ABSTRACT

A structure having an optical element thereon has a portion of the structure extending beyond a region having the optical element in at least one direction. The structure may include an active optical element, with the different dimensions of the substrates forming the structure allowing access for the electrical interconnections for the active optical elements. Different dicing techniques may be used to realize the uneven structures.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application claims priority under 35 U.S.C. § 119 to allowedU.S. application Ser. No. 09/983,278, filed Oct. 23, 2001 U.S. Pat. No.6,798,931, which in turn claims priority of U.S. Provisional ApplicationNo. 60/273,321 entitled “Separating of Electro-Optical IntegratedModules and Structures Formed Thereby” filed Mar. 3, 2001, the entirecontents of both of which are hereby incorporated by reference in theirentirety for all purposes.

FIELD OF THE INVENTION

The present invention is directed to techniques for separating moduleson a wafer, particularly for use in creating wafer level assembly ofelectro-optical modules with manageable electrical input-output, and thestructures formed thereby. The present invention is further directed toproviding a mechanical support ledge for integrating an optical modulewith another structure, e.g., a circuit board.

BACKGROUND OF THE INVENTION

One obstacle encountered in integrating electrical devices with opticalcomponents on a wafer level is how to manage the electrical connections.Typical wafer assembly and separating can yield an excellent opticalassembly, but with no feasible location for electrical connections, asshown in FIG. 1. In FIG. 1, the module includes an active element 10mounted on a submount 20 and an optics block 30 with an optical element40 thereon. Interconnection lines 22 are formed on the submount 20 toprovide electrical signals to and/or from the active element 10. Theactive element 10, e.g., a vertical cavity surface emitting laser(VCSEL), can bonded to the submount 20 at the wafer level, optics andany spacers aligned thereto and integrated therewith. When theindividual modules are separated, the electrical connections 22 to theactive element 10 are difficult to access.

Another problem arises when attempting to integrate optical elementelements formed on a wafer level with planar systems, such as a printedcircuit board, or any system which is not to continue the stackedstructure of the wafer level constructions. Support and alignment areboth issues in this integration.

One potential solution is to assemble the optics and spacers at thewafer level, then separate and bond to the individual submounts.However, this does not take full advantage of wafer level assembly.

SUMMARY OF THE INVENTION

The present invention is therefore directed to methods and structures ofproviding interconnections to electro-optical elements in anelectro-optical module formed on a wafer level which overcome at leastone of the above disadvantages.

The present invention is also directed to methods and structures ofproviding alignment and support for wafer based integrated opticalsubassemblies with non-stacked systems that overcome at least one of theabove disadvantages.

At least one of the above and other objects may be realized by providinga method of creating an electro-optic module including providing anactive element wafer having a plurality of active elements thereon;aligning a feature wafer having features thereon to the active elementwafer, providing an electrical bonding pad on at least one of the activeelement wafer and the feature wafer, attaching the feature wafer and theactive element wafer to form an integrated wafer, and separating diesfrom the integrated wafer, at least one die including at least oneactive element and a feature, said separating including separating alongdifferent vertical paths through the integrated wafer such that at leasta portion of the wafer having the electrical bonding pad extends beyondthe other wafer.

At least one of the above and other objects may be realized by providingan integrated electro-optical module including an active element on afirst substrate, a feature on a second substrate, a bonding pad on oneof the first and second substrates, the first substrate and the secondsubstrate being attached in a vertical direction to one another, aportion of the first and second substrates having the bonding padthereon extending further in at least one direction than the othersubstrate.

At least one of the above and other objects may be realized by providingan apparatus including a planar structure having a hole therein, anoptical element formed on a surface of a substrate, the surface havingthe optical element thereon extending through the hole of the planarstructure, a mounting surface, integrated with the substrate having theoptical element, the mounting surface extending in at least onedirection beyond the substrate; and an attachment mechanism securing theoptical element to the planar structure via the mounting surface.

These and other objects of the present invention will become morereadily apparent from the detailed description given hereinafter.However, it should be understood that the detailed description andspecific examples, while indicating the preferred embodiments of theinvention, are given by way of illustration only, since various changesand modifications within the spirit and scope of the invention willbecome apparent to those skilled in the art from this detaileddescription.

BRIEF DESCRIPTION OF THE DRAWINGS

The foregoing and other objects, aspects and advantages will bedescribed with reference to the drawings, in which:

FIG. 1 is a schematic perspective view of an electro-optic module whichhas been formed at the wafer level and separated in a conventionalmanner;

FIG. 2A is a schematic side view of a plurality of electro-optic modulesbefore being separated in accordance with the present invention;

FIG. 2B is a schematic side view of a plurality of electro-optic modulesof FIG. 2A after being separated in accordance with the presentinvention;

FIG. 3A is a schematic side view of a plurality of electro-optic modulesbefore being separated in accordance with the present invention;

FIG. 3B is a schematic side view of a plurality of electro-optic modulesof FIG. 3A after being separated in accordance with the presentinvention;

FIG. 4A is a schematic side view of a plurality of electro-optic modulesbefore being separated in accordance with the present invention;

FIG. 4B is a schematic side view of a plurality of electro-optic modulesof FIG. 4A after being separated in accordance with the presentinvention;

FIG. 5 is a schematic side view of a plurality of electro-optic modulesbefore being separated in accordance with the present invention;

FIG. 6A is a schematic side view of a plurality of electro-optic modulesbefore being separated in accordance with the present invention;

FIG. 6B is a schematic side view of a plurality of electro-optic modulesof FIG. 6A after being separated in accordance with the presentinvention;

FIG. 7A is a schematic side view of a plurality of electro-optic modulesbefore being separated in accordance with the present invention;

FIG. 7B is a schematic side view of a plurality of electro-optic modulesof FIG. 7A after being separated in accordance with the presentinvention;

FIG. 8 is a top view of the connection of an electro-optic module shownin FIG. 2B with a flexible printed circuit board in accordance with thepresent invention; and

FIG. 9 is a schematic top view of the mounting of an optical subassemblywith a circuit board in accordance with the present invention.

DETAILED DESCRIPTION OF THE EMBODIMENTS

In the following description, for purposes of explanation and notlimitation, specific details are set forth in order to provide athorough understanding of the present invention. However, it will beapparent to one skilled in the art that the present invention may bepracticed in other embodiments that depart from these specific details.In other instances, detailed descriptions of well-known devices andmethods are omitted so as not to obscure the description of the presentinvention with unnecessary details. As used herein, the term “wafer” isto mean any substrate on which a plurality of components are formedwhich are to be separated prior to final use.

FIG. 2A is an exploded side view of the wafer level assembly of aplurality of integrated electro-optical modules. As in FIG. 1, thesubmount wafer 20 has an electro-optical element 10 thereon withinterconnection tracks 22. An optics wafer 30 having correspondingoptical elements 40 formed thereon is also provided. A spacer wafer 50separates the optics wafer 30 and the submount wafer 20. The spacerwafer includes passages 52 therein which allow light to pass between theoptical element 40 and the active element 10. As shown in FIG. 2A, thesepassages 52 may be formed by etching when the spacer wafer 50 issilicon.

In FIG. 2A, the spacer wafer 50 also includes indentations 54, here alsoformed by etching, These indentations 54 are provided over the bond site24 so that upon separating along lines 62, 64, the bond site 24 will beaccessible in the separated module, as seen in FIG. 2B. This facilitateselectrical connections required to the electro-optical element 10. Theseparating may include dicing the optics wafer 30 and the spacer wafer50 along line 62 and dicing through all three wafers along line 64.Alternatively, a wide blade may be used to dice the entire width betweenlines 62, 64 through the optics wafer 30 and the spacer wafer 50, andthen using a thin blade to dice only the submount wafer 20. The attachedstructure may be flipped to facilitate dicing of only the submount wafer20.

An alternative configuration is shown in FIGS. 3A and 3B, in which thespacer wafer includes holes 56 therein over the bond site 24, ratherthan the indentations 54. The separating lines 65, 64 remain the sameand may be realized in either process noted above. However, theresulting structure will not have even edges of the optics wafer 30 andthe spacer wafer 50.

Another configuration is shown in FIGS. 4A and 4B. Here, rather thanforming the same active element 10—bonding site 24 pairs on the submountwafer 20, adjacent structures will be mirror images of one another. Thisallows large indentations 58 to be placed over two bonding site 24, 24′.The separating along separating line 76 may be performed in aconventional manner. Separating along separating lines 70, 72 is onlythrough the optics wafer 30 and the spacer wafer 50, and may be realizedeither by dicing along either line or with a thick dicing blade coveringthe width of the gap between separating lines 70, 72. The submount wafer20 is then separated along separating line 74, preferably using a thinblade.

FIG. 5 illustrates another configuration, requiring less separating.Here, the spacer wafer again includes the holes 56. The optics wafer 30also includes holes 36, here etched in the optics wafer 30, isolatingthe different optics needed for each module. Also as shown herein, thesubmount 20 includes two electro-optical elements 10, 12 requiringinterconnection. Here the electro-optical elements are different fromone another, with the electro-optical element 12 being monolithicallyintegrated with the submount wafer 20. Additional optical elements 42are provided on the optical wafer 30 for the electro-optical element 12.Here, only separation of the submount wafer 20 along separating line 80is required to realize the individual modules.

Another alternative is shown in FIGS. 6A–6B. Here, a bonding pad 124 isprovided on the optics wafer 30. An interconnection line 122 connectingthe active element 10 and the bonding pad 124 would be on both the mountwafer 20 and the optics wafer 30. As shown on FIGS. 6A and 6B, thebonding between the mount wafer 20 and the optics wafer 30 is via anelectrically conductive material, here shown as solder balls 90.Alternatively, the spacer used in the previous configurations could becoated with metal where needed to provide the lead from the activeelement 10 to the bonding pad 24 on the optics wafer 30. Now theseparating lines 92, 94, 96 lead to a separation of the module thatresults in the optics wafer 30 extending beyond the mount wafer 20 in atleast one direction, i.e., so that the bonding pad 124 is easilyaccessible.

Another alternative is shown in FIGS. 7A–7B. Here, one bonding pad 124is provided on the optics wafer 30 while another bonding pad 24 isprovided on the mount wafer 20. A spacer wafer 50 is also provided inthis configuration. The interconnection line 122 connecting the bondingpad 124 and the active element 10 would be on the mount wafer 20, thespacer wafer 50 and the optics wafer 30. As shown on FIGS. 7A and 7B,the interconnection line 122 follows the spacer wafer 50 between themount wafer 20 and the optics wafer 30. Alternatively, a metal or otherelectrically conductive material may be patterned on the wafer, and theinterconnection line 122 being only on the mount wafer 20 and the spacerwafer 30, with the electrically conductive material on the spacer wafer50 providing connection therebetween. Now separating lines 93, 95, 97,99 lead to a separation of the module that results in the optics wafer30 extending beyond the mount wafer 20 in at least one direction, i.e.,so that the bonding pad 124 is easily accessible, and the mount wafer 20extending beyond the optics wafer 30 in at least one direction, i.e., sothat the bonding pad 24 is easily accessible.

As shown in FIG. 8, a flexible printed circuit board (PCB) 100 may bedirectly attached to the modules formed by any of the aboveconfigurations. While the above configurations show a cross-section ofthe modules, it is to be understood that any of the electro-opticalelement—bonding site pairs may be an array thereof, as shown in module110 of FIG. 8. Due to the separating discussed above, a step 26 formedby the extension of the wafer having the bonding sites 24 thereonreadily provides electrical connection to another device, here a PCB100. Further, the module 110 may be separated to provide steps 28 in thewafer having the bonding pads 24 thereon, here shown as the mount wafer20, on either side of the other wafer, here shown as the optics wafer30, to facilitate mechanical strain relief for the flex lead of the PCB.The steps 28 may extend around the whole perimeter.

Even if electrical interconnections are not to be provided on the steps28, when integrating an optical subassembly formed on a wafer level witha system which is not t be stacked as the rest of the wafer assembly,these steps 28 may be used to provide support and/or alignment features.For example, as shown in FIG. 9, an optical subassembly 130 to bemounted in a circuit board 120 having a hole 125 therein for receivingthe optical subassembly 130 may include steps 128 to provide mechanicalsupport and/or alignment to the circuit board. The steps 128 may extendaround the entire perimeter of the optical subassembly 130. The opticalsubassembly 130 and the steps 128 may be formed on a wafer level. Thesteps 128 may include alignment features for facilitating alignment ofthe circuit board 120 and the optical subassembly 130. The steps 128 mayprovide mechanical mounting surface for mounting the optical subassembly130 to the circuit board 120. The use of the steps 128 for attachmentalso allows the bonding material to be kept out of the optical plane.

It will be obvious that the invention may be varied in a plurality ofways, such as the use of different bonding materials, extension in oneor more directions, and different, or no, spacer configurations. Suchvariations are not to be regarded as a departure from the scope of theinvention. All such modifications as would be obvious to one skilled inthe art are intended to be included within the scope of the appendedclaims.

1. An integrated electro-optical module, comprising: an active element on a first substrate; a feature on a second substrate; a bonding pad on one of the first and second substrates; a spacer substrate between the first substrate and the second substrate in a vertical direction, a portion of the first and second substrates having the bonding pad thereon extending further in at least one direction than the other substrate; and an electrical interconnection extending from the active element to the bonding pad through the means for attaching.
 2. The integrated electro-optical module of claim 1, wherein the first and second substrates are attached via the spacer substrate.
 3. The integrated electro-optical module of claim 1, wherein the electrical bonding pad is on the first substrate.
 4. The integrated electro-optical module of claim 1, wherein the bonding pad is on the second substrate.
 5. The integrated electro-optical module of claim 4, further comprising an electrically conductive material between the first and second substrates.
 6. The integrated electro-optical module of claim 5, wherein the electrically conductive material includes solder balls.
 7. The integrated electro-optical module of claim 5, wherein the electrically conductive material is on an element between the first and second substrates.
 8. The integrated electro-optical module of claim 1, wherein the features are optical elements.
 9. The integrated electro-optical module of claim 1, wherein the features are holes.
 10. The integrated electro-optical module of claim 1, wherein the features are indentations.
 11. The integrated electro-optical module of claim 1, wherein the means for attaching hermetically seals the active element.
 12. An integrated electro-optical module, comprising: an active element on a first substrate; a feature on a second substrate; a bonding pad on one of the first and second substrates; means for attaching the first substrate and the second substrate in a vertical direction to one another, a portion of the first and second substrates having the bonding pad thereon extending further in at least one direction than the other substrate; an electrical interconnection extending from the active element to the bonding pad through the means for attaching, the electrical interconnection including conductive material between the first and second substrates.
 13. The integrated electro-optical module of claim 12, wherein the electrically conductive material includes solder balls.
 14. The integrated electro-optical module of claim 13, wherein the electrically conductive material is on an element between the first and second substrates.
 15. The integrated electro-optical module of claim 12, wherein the means for attaching hermetically seals the active element.
 16. The integrated electro-optical module of claim 12, wherein the features are optical elements.
 17. The integrated electro-optical module of claim 12, wherein the features are holes.
 18. The integrated electro-optical module of claim 12, wherein the features are indentations.
 19. The integrated electro-optical module of claim 12, wherein the electrical bonding pad is on the first substrate.
 20. The integrated electro-optical module of claim 12, wherein the bonding pad is on the second substrate. 